EP0859468B1 - Circuitry for a sensor element - Google Patents

Abstract

A circuit arrangement (11) has an activating circuit (13) for a sensor element (12) of a touch contact switch, which in one embodiment of the invention contains a frequency generator (16). The frequency generator (16) generates a frequency-modulated activating signal (17), which is applied to the sensor element (12). In another embodiment the forming of the activating signal (17) takes place in a microcontroller (48), containing eventually the activating part (13) and or the evaluation of the signal. Through passing through a large frequency range for the activating signal (17), the influence of extraneous signals, even when using a lower signal voltage, is minimized.

Description

Field of application and state of the art

The invention relates to a circuit arrangement for at least one Sensor element of at least one touch switch, in which a Control signal is present at the sensor element and depending on the actuation state of the sensor element is changeable, which Control signal is frequency modulated.

Touch switches are used in many electrical devices today used, especially in household appliances. With a simple tap of the switch, which usually has a metal surface a desired switching operation can be triggered by the user.

In known touch switches that have a sensor element, a circuit is provided, which is usually connected to the sensor element high-frequency AC voltage applied when the touch switch is actuated is changed. This change is detected and triggers a switching signal. However, there are significant problems with this Interferences that interfere with the signal. These disturbances stir on the one hand because of the power supply from the network the increasing number of electrical devices the so-called electrosmog has increased significantly, which means that the mains voltage numerous interference signals are superimposed. Other devices shine in the same way, especially in the household, like televisions, computers but also cell phones, Interference signals, all of which also come from the user Interfering with the signal on the sensor element.

For this reason, attempts have already been made to increase the amount invested Signal voltage of 5 V (usual supply voltage electronic Circuits) to generate a stronger signal at 20 to 30 V, that is insensitive to interference. On the one hand, that means the need for a second power supply, on the other but this also did not completely solve the problems become.

EP 675 600 discloses in a circuit arrangement according to the The preamble of claim 1 is a reflective touch switch on an ultrasound basis, in which the reflection characterizing the touch of a signal is detected by a piezoelectric element. At the same time, this piezoelectric element sends the control signal out. The control signal is through the piezoelectric element amplitude modulated. To detect a triggering of the switch the received signal is demodulated.

US-A-5 270 710 shows a drive circuit for a switch which is actuated in that two contacts by a compressible electrically conductive shell are connected to each other. A control signal is due to a contact. The other contact is via a capacitor and a diode to an evaluation circuit. Negative half-waves of the control signal applied to a contact are automatically switched on for this half-wave by a diode Mass closed.

Task and solution

The object of the invention is to provide an improved circuit arrangement for to create a sensor element of a touch switch that against Interference signals are insensitive and in particular without additional power supply gets along.

This object is achieved by the features of claim 1. In particular this can be the zero voltage. The zero phase is preferred of the control signal set to zero. This eliminates interference signals in occur during this phase and when the zero phase is superimposed particularly annoying, suppressed in a simple manner. The signal is therefore at least partially cleaned up.

The control signal preferably runs through a certain periodically Frequency range, causing interference signals, each a specific fixed Have frequency, occur only very briefly in sync with the control signal. Because the evaluation can be carried out so that it only over a longer period or a certain frequency range Changes in the signal level that occur as changes in the switching state recognizes, interfering signals play with another or one fixed frequency doesn't matter. Interference signals also occur mostly only in certain frequency ranges, and at Pass through a wide, much larger frequency range these areas are only briefly covered.

The circuit arrangement consists of at least one control, a sensor and an evaluation part, in particular each sensor element has an associated sensor part, preferably has a sensor circuit. Through this Splitting it is possible to use multiple touch switches only to combine a control and an evaluation part. at the number of components and thus can be fully functional reduce effort and susceptibility to errors.

A working frequency generated in the control part can preferably be used with a fixed frequency deviation periodically changeable lie between a minimum value and a maximum value, the minimum value in particular being approximately 5 kHz and the maximum value can be approximately 50 kHz. The modulation frequency can advantageously be about 20 to 1000 Hz. By the wide frequency range from 5 kHz to 50 kHz ensures that sufficient areas are traversed in which have no interference signals. Especially low frequency Interferences, for example harmonics of the Mains frequency are excluded. The fixed modulation frequency ensures that the frequency range is sufficient will go through quickly. The effort for this Frequency generation is slightly larger than for a fixed one Output frequency.

The control signal is particularly preferred as a square-wave signal, especially as a square wave signal with a duty cycle from about 70% to 95% and / or a signal level of about 5 V, formed. The high duty cycle ensures that the duration of the zero level is not too long, so that the most The resulting DC voltage is sufficiently high. By the use of a signal level of 5 V can be used for the electronic components used operating voltage use and does not need any further power supply. In order to the effort is reduced, the operational safety becomes increased and interference from another power supply are avoided.

A component, in particular a feed capacitor, advantageously forms part of a voltage divider, in particular a capacitive voltage divider, the sensor element forms the other or second part of the voltage divider. The touch switch is above the user's finger capacity can be actuated, and therefore offers a capacitive Voltage divider. With such a voltage divider in a very simple way by monitoring the partial voltages a change in one of the two capacities, in this case the capacity of the sensor can be detected. The feed capacitor preferably has a constant capacity on.

To control multiple sensor parts with a single one To enable control part is the component that the forms the first part of the voltage divider in the sensor part contain. Via branch lines from a feeder node the sensor parts can be connected to the control part, so that the same control signal at all sensor parts is applied.

A filter, in particular, is preferred for the output of the sensor part an R-C filter, upstream. Through this filter the signal of the sensor element becomes a DC voltage converted by the duty cycle, the signal level and the Actuation state of the touch switch depends. Since the first two sizes are fixed can be evaluated the DC voltage, an actuation of the touch switch can be detected. Such a filter is easy build up and the resulting DC voltage is simple Evaluate means. It is advantageous in every sensor part a filter is provided to avoid interference.

In one embodiment of the invention, the switching means contain a switch, in particular a switch with a semiconductor device. The semiconductor device can for example, be a transistor or another, quickly responsive component.

According to a further embodiment of the invention the control part has a frequency generator for generation of the frequency-modulated control signal with the operating frequency on. The effort for such a frequency generator is not much larger than for one with a fixed one Working frequency because such frequency generators in others Areas of application are common.

If two inverting components are used to control the switch in succession at any point in the signal path behind the frequency generator and in front of the sensor element, for example in front of a feed capacitor, where the simply inverted signal at the output of the first inverting component is guided to the switch and its control forms an automatic coupling of the switch and its function to the working frequency guaranteed. By connecting two inverters in series you get the unchanged at the exit of the second Drive signal. The inverters work quickly and reliably and are not a source of error.

The evaluation section provides instructions for evaluating several signals a signal multiplexer with at least one at its input Input for connecting at least one output of a sensor part and an output on which via a signal amplifier a signal evaluation unit, in particular a microcontroller, connected. So you only need a signal evaluation unit for all sensor elements used and the Effort is reduced.

According to one embodiment of the invention, the Circuit arrangement contain at least one microcontroller, which among other things for the generation of the control signal with the working frequency for at least one sensor element is set up. Such a software generation provides an arbitrarily variable control signal, which enables a wide range of applications. In this way, an additional frequency generator can be saved, which saves costs and the susceptibility to failure lowers. The microcontroller is advantageous for other purposes can be used in addition to frequency generation, so for the evaluation of the sensor signal or completely different control tasks in a device belonging to the touch switch.

In one embodiment, a microcontroller preferably contains Control part and evaluation part of the circuit arrangement. The further reduces the effort and enables an exact evaluation of the signal present at the sensor element. Advantageous can also use the switching means in the microcontroller be included, one for shorting each Phase of the control signal applied to the sensor element a constant voltage, preferably the zero voltage, is formed are. This increases the number of components required reduced to a minimum, which also affects the susceptibility to errors has a positive effect. A measurement method is available AD measurement, whereby the AD conversion by dualslope method, Single slope method (with a comparator in the microcontroller) or can be done by your own AD converter. This is preferably contained in the microcontroller. However, the AD conversion by dual slope method is preferred applied.

A particularly favorable embodiment of the invention provides that the sensor element is a flexible, spatial shape changeable and is electrically conductive body and in particular for use in a touch switch Tempered glass or glass ceramic hob is provided. Prefers it is an electrically conductive foam. The use of such a sensor element for this purpose offers a number of advantages. The sensor element can have material properties that occur from suppressing interference.

The body of the sensor element can at least advantageously have a breakthrough in the direction of the contact surfaces, in which in particular by a hard glass or glass ceramic hob visible lighting element is included. This can for example be an LED with which the exact position the touch button can be displayed.

These and other features go beyond the claims also from the description and the drawings, wherein the individual features individually or separately several in the form of sub-combinations in one embodiment of the invention and in other fields be and advantageous as well as protective designs can represent, for which protection is claimed here. The division of the application into individual sections as well Inter-headings limit those made under them Statements not in their general validity.

Brief description of the drawings

Fig. 1

eine Schaltungsanordnung, bestehend aus Ansteuer-, Sensor- und Auswerteteil, mit einem an einem Glaskeramikkochfeld angebrachten Sensorelement,

Fig. 2

die Schaltungsanordnung mit einem Mikrokontroller, der Ansteuer- und Auswerteteil enthält,

Fig. 3 bis 5

ein üblicherweise verwendetes Sensorelement zum Einbau an ein Glaskeramikkochfeld und

Fig. 6 bis 8

ein neuartiges Sensorelement nach einem Merkmal der Erfindung zum Einbau an ein Glaskeramikkochfeld.

An embodiment of the invention is shown in the drawings and is explained in more detail below. The drawings show:

Fig. 1

a circuit arrangement consisting of control, sensor and evaluation part with a sensor element attached to a glass ceramic cooktop,

Fig. 2

the circuit arrangement with a microcontroller which contains the control and evaluation part,

3 to 5

a commonly used sensor element for installation on a glass ceramic hob and

6 to 8

a novel sensor element according to a feature of the invention for installation on a glass ceramic hob.

Description of a preferred embodiment

1 shows a circuit arrangement 11 for a sensor element 12, which consists of a control part 13, a sensor part 14 and an evaluation part 15. The control part 13 contains a frequency generator 16 which provides a drive signal 17 generated with an operating frequency that at an output 18th of the frequency generator 16 is output and from a frequency-modulated square wave signal. It becomes one led first inverter 19 and from there to a second Inverter 20. Then it goes through a feed resistor 21 a feed node 23, of which a first branch line 24 goes to which a number of sensor parts 14 connected can be, of which only one is shown. Of the first branch line 24 goes through a connection Feed capacitor 22 to a signal node 25 in the sensor part 14 from.

There is a branch 26 behind the first inverter 19, which leads to a switch node 27. From the switch node 27 goes off a second branch line 28 to which a plurality can be connected by switches 29. Everyone Sensor part 14 contains a switch 29 on its one Switch connection with the signal node 25 and at its other Switching connection with the zero level of the circuit arrangement 11 connected to ground.

From the signal node 25 a connection goes to the connection of the Sensor element 12, the connection through a printed circuit board 38 takes place on which the sensor element 12 sits, see FIG. 4 or 7. The structure of the sensor element 12 can be seen in FIG. 3 be removed. A spring element goes from the printed circuit board 38 30, which must be conductive and preferably as a metallic Spring is formed upwards and carries a Sensor guide plate 31 by a spring element 30 against Tempered glass or glass ceramic hob 34 is pressed. The Sensor element 12 has a stray capacitance 33 that opposes Crowd goes.

Due to the mechanical coupling of the sensor element 12 the glass ceramic hob 34 creates an air gap capacity 35, since the coupling is caused by a manufacturing Nub 32 on the underside of the glass ceramic hob 34 is provided with an air gap 36. This is shown in Fig. 5 in Magnification shown.

The capacity of the glass ceramic hob 34 is determined by a Glass capacity 37 shown. 4 shows one Finger 39, which the glass ceramic hob 34 above the Touches sensor element 12. This results in glass capacity 37 add a serial finger capacitance 40 that goes to ground.

A connection goes to a filter 41 from the signal node 25, that as an R-C filter from a serial filter resistor 42 and a filter capacitor 43 that goes to ground. A connection goes from the filter 41 to an output 44 of the sensor part 14.

This output 44 of the sensor part 14 goes to one of several inputs 45 of a signal multiplexer 46. Der Signal multiplexer 46 is on via a signal amplifier 47 a signal evaluation unit, in particular a microcontroller 48 connected. These three components form the evaluation part 15, to which so many sensor parts 14 are connected can be how the signal multiplexer has inputs. The microcontroller is not with an output 49 to one shown part of a circuit connected by the Microcontroller implements commands generated, for example for a power cut-off or connection of an electric cooker.

2 shows an embodiment with generation of the Control signal shown in the microcontroller 48. The Control signal 17 is a common connection A0 Series resistor and individual feed capacitors 22 and resistors 53 given to the sensor element 12. In In this drawing, the sensor element 12 is more variable Capacitor shown, the change in capacitance by touching the touch switch. simultaneously are the resistors 53 with the sensor elements 12 further resistors 54 and capacitors 55 to ground placed.

The connections L0 and L1 are used to discharge the Capacitors 55, the resistors 54 an RC element form. The evaluation of that applied to a sensor element 12 Control signal 17 takes place via connections of the Connections I0 and I1 to the capacitors 55 of the RC element.

As shown, the microcontroller 48 combines both Control part 13 and the evaluation part 15. The sensor part 14 is from the sensor elements 12 and the feed capacitors 22, the resistors 53 and 54 and the capacitors 55 formed. Depending on the type of microcontroller used 48 a different number of sensor parts 14 or Sensor elements 12 are operated.

An equivalent circuit diagram of one made of an electrically conductive and flexible foam existing sensor element 12 seen in Fig. 6. It can be characterized by a parallel connection an equivalent resistor 50 with a serial inductive Resistor 51 and a parallel capacitance 52 shown become.

7 is a between the circuit board 38 and the glass ceramic hob 34 attached sensor element 12 shown that made of an electrically conductive and flexible foam consists. In Fig. 8 it can be seen that the sensor element 12 so well on the nubbed underside of the glass ceramic hob 34 adjusts that the formation of an air gap 36th is avoided.

function

At this point we will start with the execution with frequency generator received. The circuit is done according to the circuit diagram 1, preferably in SMD technology and on the circuit board 38, which is also the support and at the same time forms the connection for the sensor element 12. The Using a 5 V signal level has the great advantage that only a 5 V power supply is required because this is the operating voltage of the signal multiplexer 46 and Microcontroller 48 is.

The frequency generator 16 first generates a square wave signal a signal level of 5 V, a duty cycle of about 70 up to 95% and a frequency of 20 to 500 kHz. This Square wave is with a modulation frequency of 20 to 1000 Hz frequency modulated, between basic parameters of typically 5 to 50 kHz. This gives you the control signal 17th

The first inverter 19 is used to control the switch 29 needed. If the drive signal 17 goes back to zero, so it is inverted by the inverter 19 and set to 5 V, and by this raising the switch 29 is activated and closes the signal node 25 to ground. So that's the Signal node 25 lying signal always zero when that Control signal 17 is zero. Faults are so during suppressed this time. Through the second inverter 20 behind the first becomes the original output signal 17 manufactured. This goes through the feed resistance 21 and Branch line 24 to the feed capacitor 22.

In the unactuated state, the sensor element 12 only has its Stray capacitance 33, the one with the feed capacitor 22 Voltage divider for the output signal applied to the supply capacitor forms. The feed capacitor 22 can do so be dimensioned so that half the voltage on the sensor element 12 is present, so the food capacity is approximately as large like the stray capacitance 33. When the touch switch is actuated come in parallel to the stray capacitance 33 Air gap capacity 35, the glass capacity 37 and the finger capacity 40, which are connected in series. Through this Parallel connection is the total capacity of the sensor element 12 larger, the division ratio of the total capacity to Capacitance of the feed capacitor 22 changes, and the Tension on the sensor element and thus on the signal node 25 takes from. At the output of the connected to the signal node 25 Filters 41 sets a DC voltage that only from predetermined signal level, the duty cycle that is known and is unchangeable, and from the sensor voltage, which from Actuation state of the touch switch is dependent, depends.

This DC voltage is sent to a signal multiplexer 46 given one of several DC voltages of several Selects sensor circuits 14 and this via a signal amplifier 47 to a microcontroller 48 there. The microcontroller 48 evaluates the DC voltage and detects whether the touch switch has been operated or not. It is the evaluation preferably designed so that over a certain period, corresponding to one in that period swept frequency range, for example adding up or is evaluated integratively. So only if a change in DC voltage above that certain The evaluation should take place over a period of time Report. Now an interference signal occurs with a fixed Frequency, the DC voltage changes, if at all just for a moment and that falls within for the evaluation of the planned period does not matter. Of the microcontroller indicates a detection its output 49 commands to another circuit, for example the control circuit for a hob heating.

The equivalent resistor 50 forms with the feed capacitor 22 and the stray capacitance 33 a filter that the coupling of interference signals via the finger 39 when the Touch switch dampens. To the material of the sensor element 12 to make conductive, different materials, e.g. Graphite, silver or the like be added. If one instead or in addition ferritic materials admixed, the inductive resistor 51, the one further improves the attenuation of interference signals. One that is submitted at the same time is particularly advantageous European patent application EP 859 467 entitled "Touch switch with sensor key" shown and described Sensor element. In this way, such Sensor element a particularly inexpensive version of the Invention to be created. You can equally at used two versions of the generation of the control signal become.

The embodiment according to FIG. 2 controls the sensor element 12 according to the following scheme:

In the first step, the RC element from the resistor 54 and discharge capacitor 55 through terminal L0. In the second The capacitor 55 will step through the terminal L0 so long charged until a logic high level is measured at input I0 becomes. In practice this is the case if the Capacitor 55 to the general operating voltage of 5 volts is charged.

In step 3, this is at port A0 for a certain time Control signal 17 with the modulation according to the invention or Generates frequency modulation and thus the capacitor 55 over discharge resistor 54. The control signal can essentially the same as the version with frequency generator. In this phase, the connection L0 is made before each change of the Signals from low to high at A0 high impedance and before the change from high to low at A0 low resistance against the zero voltage connected. In this way, this is done with this version Grounding during the zero phase of the control signal.

In step 4, the RC element of resistor 54 and capacitor 55 recharged via connection L0. Doing so measured the time until the signal at connection I0 reaches the High level changes. As mentioned above, the AD conversion takes place of the signal present at connection I0 or I1 preferably in the dual slope method. The evaluation of the voltage applied to the sensor element can preferably be dynamic take place, causing a temperature drift of the signal level can be compensated.

Just as in the embodiment of FIG. 1 here the change in the control signal 17 by touching the sensor element 12 thus supplied. One of them resulting switching process can be done exactly the same.

Claims (10)

1. Circuit arrangement for at least one sensor element (12) of at least one contact switch in which a control signal (17) is applied to the sensor element with a working frequency and is variable depending on the actuation state of the sensor element, where the control signal is a frequency-modulated control signal, characterized by switching means (29) which are designed for short-circuiting one phase each of the control signal (17) applied to the sensor element (12) to a constant voltage.
2. Circuit arrangement according to Claim 1, characterized in that the circuit arrangement (11) comprises at least one control part (13), one sensor part (14) and one evaluation part (15), where in particular each sensor element (12) has an associated sensor part (14).
3. Circuit arrangement according to Claim 1 or Claim 2, characterized in that the working frequency with a fixed frequency deviation is periodically variable between a minimum and a maximum value.
4. Circuit arrangement according to one of the preceding claims, characterized in that the control signal (17) is a rectangular signal, in particular a rectangular signal, with a duty factor of around 70 % to 95 % and a signal level of around 5 V.
5. Circuit arrangement according to one of the preceding claims, characterized in that a component (22) forms a first part of a voltage divider and the sensor element (12) the second part of the voltage divider, where in particular the component (22) forming the first part of the voltage divider is contained in the sensor part (14).
6. Circuit arrangement according to one of the preceding claims, characterized in that the switching means are designed for short-circuiting one phase each of the control signal (17) applied to the sensor element (12) to the zero voltage, where the switching means contain preferably one switch (29), in particular a switch with a semiconductor component.
7. Circuit arrangement according to one of the preceding claims, characterized by a frequency generator (16) for generating the frequency-modulated control signal (17) with the working frequency, where for control of the switching means (29) two inverting components (19, 20) are preferably provided one behind the other at any point in the signal path behind the frequency generator (16) and in front of the sensor element (12), and where the signal inverted once after the first inverting component (19) is passed at the output of this component (19) to the switching means (29) and provides their control.
8. Circuit arrangement according to Claim 2, characterized by a signal multiplexer (46) with at least one input (45) for connection of at least one output (44) of a sensor part (14) and with an output to which a signal evaluation unit (48) is connected via a signal amplifier (47), where in particular the signal multiplexer (46) is contained in the evaluation part (15).
9. Circuit arrangement according to one of Claims 1 to 6, characterized by at least one micro-controller (48) which is designed for the generation of at least the control signal (17) with the working frequency for at least one sensor element (12), where said micro-controller contains in particular the control part (13) and/or the evaluation part (15) and the switching means (29).
10. Circuit arrangement according to one of the preceding claims, characterized in that the sensor element (12) is a per se flexible, shape-variable and electrically conductive element, preferably comprising electrically conductive foam material, intended in particular for use in a contact switch of a hard glass or glass ceramic hob (34).

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